The present invention relates generally to resilient articles, such as sanding sponges. More particularly, the present invention relates to an abrasive article having a flexible make coating and a thin, hard, anti-loading size coating.
Coated abrasive articles are normally prepared by coating at least one surface of a substrate with a first adhesive binder layer, often referred to as the xe2x80x9cmakexe2x80x9d coating. Particles of abrasive material are applied to the coated substrate xe2x80x9csizexe2x80x9d coating, is then applied over the abrasive particles and make coating. Typical abrasive coatings generally include a make coating, abrasive particles, and a size coating. Anti-loading materials have also been included in a further optional layer, referred to as a xe2x80x9csuper-sizexe2x80x9d coating, which prevents buildup on the abrasive surface and, therefore, increases the useful life of the article.
Resilient or conformable abrasive articles, such as sanding sponges, are known in the prior art. Such abrasive articles have been found useful in cleaning, polishing, abrading, and dimensioning materials such as wood, metal, plastic, and the like, especially when such materials have and are to retain irregular, relieved, or otherwise intricate surface contours, or, when the manual control of working pressures between the abrasive article and the workpiece is desirable, such as when smoothing interior drywall surfaces.
To maintain the resilient properties of the abrasive article, flexible elastomeric binders are often used to adhesively bond the abrasive particles to a major surface of the foam substrate. In addition to using elastomeric binders, most conventional resilient abrasive articles are constructed so that each coating layer is at least as flexible as the underlying coating layer. Thus, for a typical resilient abrasive article having a make coat applied to a resilient foam substrate, abrasive particles embedded in the make coat, and a size coat applied over the make coat and abrasive particles, the size coat would be at least as flexible as the make coat. Such a configuration allows the abrasive article to maintain its flexibility and prevents the abrasive coating from cracking or splitting as the abrasive article is run over sharp corners or edges of a work surface during use. Flexible make and size coats, however, are soft and therefore do not provide adequate lateral support for the abrasive particles. As a result, the particles tend to tilt relative to the foam substrate as the abrasive article is pressed and moved along the work surface, thereby greatly reducing the effectiveness of the abrasive article. In addition, the soft size coat tends to rapidly buildup with swarf which shortens the useful life of the abrasive article.
Hard or rigid size coats are desirable because they provide lateral support for the abrasive particles which increases cut, and because they reduce buildup which increases the life of the article. However, when hard, non-elastomeric binders such as phenol-formaldehyde condensates are coated onto foam substrates, the resilient qualities of the foam substrates are quickly overcome by the physical properties of these binders, rendering the resultant abrasive article brittle and susceptible to cracking, tearing, and puncturing under normal use. The cracking and tearing of the abrasive article produces an inconsistent finish on the work surface and leads to premature failure of the abrasive article. To avoid the problems associated with hard size coats, most commercially available resilient abrasive articles either have been formed without a size coat or have been formed with a size coat that is at least as flexible as the make coat.
The Ruid et al. U.S. Pat. No. 4,629,473 discloses a resilient abrasive polishing product including a primary backing, a resilient layer laminated to the primary backing, and abrasive particles embedded in an elastomeric make coat on the side of the resilient layer opposite the primary backing. The product can also include an intermediate coating between the resilient layer and the elastomeric make coat, and a phenolic resin sizing adhesive layer. The primary backing can be formed of a finished cloth, paper, vulcanized fiber, non-woven webs, or plastic film. These materials are relatively inelastic and therefore prevent the resilient layer, elastomeric make coat, and size coat from stretching or elongating. This, in turn, prevents the size coat from cracking and resilient layer from tearing. The backing, however, significantly adds to the overall cost of the product. In addition, the resilient layer is formed of a thin reticulated foam layer having a thickness of 1.44 to 2.41 millimeters. Having a thin resilient layer further adds to the inflexibility of the product and makes it unsuitable for many finishing applications.
It would therefore be desirable to provide a resilient abrasive article having a resilient elongatable foam substrate thick enough to conform to a contoured surface, abrasive particles adhesively bonded to the substrate with a flexible make coat, and a hard, relatively inflexible, size coat applied over the abrasive particles and flexible make coat. More specifically, it would be desirable to provide a resilient abrasive article having a hard size coat to provide lateral support for the abrasive particles and resist swarf buildup, but which does not suffer from the cracking problem associated with conventional resilient abrasive articles having a hard size coat. It would also be desirable to provide such a resilient abrasive article which does not require an inelastic backing to prevent such cracking.
In describing the present invention, xe2x80x9cresilientxe2x80x9d refers to a property of a material that enables it to substantially recover its original shape after being bent, twisted, stretched, or compressed.
xe2x80x9cResilient abrasive articlexe2x80x9d refers to an abrasive article that does not result in knife-edging of the abrasive coating when the abrasive article is folded onto itself with the abrasive surface out. Knife-edging occurs when the abrasive coating cracks and de-laminates from the foam substrate, thereby producing sharp knife-like edges that can scratch the work surface.
xe2x80x9cMake coat precursorxe2x80x9d refers to the coatable resinous adhesive material applied to the coatable surfaces of the open cells of the foam substrate to secure abrasive particles thereto. xe2x80x9cMake coatxe2x80x9d refers to the layer of hardened resin over the coatable surfaces of the open cells of the foam substrate formed by hardening the make coat precursor.
xe2x80x9cSize coat precursorxe2x80x9d refers to the coatable resinous adhesive material applied to the coatable surfaces of the open cells of the foam substrate over the make coat. xe2x80x9cSize coatxe2x80x9d refers to the layer of hardened resin over the make coat formed by hardening the size coat precursor.
In referring to the binder compositions of the make and size coats, xe2x80x9clabilexe2x80x9d means a foamed or frothed condition imparted to a liquid dispersion of binder material (e.g., a make coat precursor or a size coat precursor) so that the frothed state of the binder dispersion is transitory. By the term xe2x80x9cfrothxe2x80x9d, it is meant a dispersion of gas bubbles throughout a liquid where each bubble is enclosed within a thin film of the liquid. The labile foams utilized in the invention thus also encompass unstable foam consisting of relatively large bubbles of gas.
Swarf refers to the fine particles that are created during the abrading process. Anti-loading refers to the ability of a coating to resist the accumulation of swarf.
The present invention provides a resilient abrasive article including a resilient, conformable, elongatable substrate having an outer surface, a flexible make coat applied to at least a portion of the outer surface of the substrate, abrasive particles embedded at least partially within the make coat, thereby adhesively bonding the abrasive particles to the substrate, and a hard size coat covering the abrasive particles and flexible make coat. To minimize the likelihood of tearing the foam substrate, the hard size coat is formed as a very thin layer having a dry add-on weight of less than approximately 15 grains/24 in2 (63 grams/m2).
The abrasive article can further include a flexible barrier coat adjacent the substrate. Alternatively, the abrasive article can include abrasive particles adhesively bonded to the substrate with a flexible adhesive make coat, a flexible size coat applied over the abrasive particles and make coat, and a hard super-size coat applied over the flexible size coat. Another embodiment can include a flexible make coat applied to the foam substrate, abrasive particles embedded in a hard size coat applied over the flexible make coat, and a flexible super-size coat applied over the hard size coat and abrasive particles.
Suitable materials for forming the substrate include polyurethane foam, foam rubber, silicone, and natural sponge. Suitable material for forming the make coat or flexible size coat include nitrile rubber, acrylic, epoxy, urethane, polyvinyl chloride, and butadiene rubber. The abrasive particles can be aluminum oxide, silicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet, ground glass, quartz, and combinations thereof. Suitable material for forming the hard size coat include phenolic resins, aminoplast resins having pendant (xcex1,xcex2-unsaturated carbonyl groups, urethane resins, epoxy resins, ethylenically unsaturated resins, acrylated isocyanurate resins, urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins, acrylated epoxy resins, bismaleimide resins, fluorene-modified epoxy resins, and combinations thereof
The make coat precursor can be applied to the foam substrate using known coating techniques including knife coating, die coating, liquid roll coating, or spraying. The size coat can be formed by frothing the size coat precursor and applying the frothed size coat precursor to the make coat, or the size coat precursor can be sprayed directly onto the make coat.